A computer is often connected to one or more peripheral devices, such as hard disk drives, tape drives, CD-ROM drives, and so forth. A popular interface for connecting such peripheral devices is the Small Computer Systems Interface (SCSI). SCSI is a parallel interface which connects up to seven peripheral devices to the computer in series in a daisy chain, called herein an SCSI chain.
The computer sends data to a given peripheral device by sending the appropriate data signals down the SCSI chain. When the data signals reach the last peripheral device at the end of the SCSI chain, they return in the other direction. This results in an imbalanced impedance in the SCSI chain. The imbalanced impedance prevents the peripheral devices from functioning correctly. Typically, this problem has been solved by providing "terminators" to the SCSI chain. The terminators absorb the data signals and maintain a balanced impedance on the SCSI chain.
In order for the computer and peripheral devices on the SCSI chain to function correctly, a normal "termination status" must be maintained. That is, exactly two terminators must be present, one on the first peripheral device and one on the last peripheral device in the SCSI chain. The termination status of the SCSI chain can change, however. When peripheral devices are added to or removed from the SCSI chain, for example, too many or too few terminators may remain. As a result, the computer and/or peripheral devices can malfunction or even shut down entirely.
When a malfunction or shutdown does occur in the computer system, it becomes essential to determine whether an incorrect termination status is the cause. If so, it is further essential to determine whether the problem is the result of having too few or too many terminators in the SCSI chain, an absence of termination power, or a different problem altogether. This determination can be a lengthy and complicated process, often requiring the examination of each peripheral device by a skilled engineer. In many instances, it is not feasible to maintain the engineer at the site of the computer system, and thus a time-consuming relocation is required whenever such a malfunction or shutdown occurs.
Many businesses depend on the continued operation of a computer system such as the one described above. Thus, the time wasted in diagnosing a computer or peripheral malfunction or shutdown in the manner described above can be very costly. Therefore, there is a need for a more efficient way to determine the termination status of peripheral devices.